A device of this generic type is used in non-delayed overcurrent releases such as, in circuit breakers for switching and protection of motors and other loads. These non-delayed overcurrent releases are designed as electromagnetic releases, which essentially include a coil winding, a coil former, an armature, a pole, a plunger, a restraining spring and a yoke. The armature pulls in at a specific circuit breaker rated current, for example at twelve times the rated current for motor protection or at 19 times the rated current for transformer protection. The armature movement in the process acts on a switch mechanism and on a moving switching piece, in order to open the contacts. According to the Standard (IEC60947), the response current must not fluctuate by more than ?20% in this case.
If the adjustment ranges are relatively wide, it is difficult to position the coil winding accurately this is because of to the relatively large supporting cross-sections required, the relatively small numbers of turns, the relatively wide tolerances for the coil and the winding wire and the relatively inhomogenous magnetic field associated with this. Thus, it is difficult; and to position the coil winding sufficiently accurately with respect to the airgap between the armature and the pole in order to make it possible to comply with the response limits in accordance with the Standard. Furthermore, there is a problem in fixing the coil winding in the position with respect to the airgap once this has been determined so that the coil winding is not moved in the direction of the center of gravity of the iron at the rated current or in the event of high short-circuit current; or with the coil being compressed or deformed as a consequence, it often results in no longer complying with the response limits.
For relatively low switching ratings; the coil winding is wound on a coil former. At the upper and lower ends, the coil former is provided with a flange, against which the winding wire rests. Furthermore, the coil formers are generally wound with a number of layers, and the last layer is bound with adhesive tape in order to fix it The coils thus form a compact unit, avoiding the problems mentioned above.
For higher switching ratings, the coils are produced with the winding turns resting on them in order to prevent the coil from being compressed and deformed in the event of high short-circuit currents.
Owing to the use of standard coil formers for the respective size and the fact that they are designed for the geometrically largest coil winding, there is often a gap between the coil former flange or yoke and the last turn of the coil winding. Once the coil winding has been positioned accurately with respect to the airgap between the armature and the pole, one end of the winding is bonded to the coil former flange or yoke in order to fix the coil winding, and the other end of the winding is welded to a connection.